The invention relates to a video signal processing apparatus in an image display apparatus which can display a video image having a different aspect ratio onto a screen or a cathode ray tube (hereinafter, abbreviated to a CRT) of a wide aspect of 9:16 of a high definition television receiver, a video projection system (hereinafter, abbreviated to a VPS), or the like. When a video image having such a different aspect ratio is displayed, the invention enables such a video image to be displayed as large as possible.
In recent years, as the number of video softwares, particularly, softwares of movies has been increased, the number of softwares of the vista size or cinema size also increases. If such a video software is displayed onto the CRT having an aspect ratio of 3:4 of the television receiver of the NTSC system, blanks occur in the upper and lower portions of the screen. The number of video images of the wide aspect ratio for the high definition television receiver or the like will increase in future. Therefore, an efficient display method is being examined.
FIG. 1 is a schematic block diagram of a clear vision (EDTV: Extended Definition Television).
In the diagram, reference numeral 1 denotes a selector for selecting and outputting one of a plurality of video sources V.sub.1 to V.sub.4 ; 2 an AGC circuit to always keep an amplitude of a video (luminance) signal constant; 3 a chroma demodulating circuit to demodulate a chrominance signal included in the video signal; 4 an A/D converting circuit to analog-digital convert the video (luminance) signal and the chrominance signals; 5 a signal processing circuit to produce interpolation signals which are necessary for the three-dimensional Y/C separation, motion detection, and double-speed sequential scan which are needed to the EDTV; 6 a memory circuit to execute the double-speed sequential scan; 7 a PLL circuit to generate clocks for the A/D conversion and clocks necessary for the double-speed sequential scan; 8 a control circuit which receives an output of the PLL circuit 7 and produces various kinds of control signals; 9 a D/A converting circuit to convert a digital video signal which has been converted into a double-speed signal by the memory circuit 6 into an analog signal; and 10 a matrix circuit to convert D/A converted luminance signal (2Y) and chrominance signals (2I, 2Q) into primary color signals of R, G, and B.
The operation of the EDTV constructed as mentioned above will now be briefly described hereinbelow.
One of the video signals in the video source selected by the selector 1 is supplied as a luminance signal to the AGC circuit 2 and is subjected to the AGC so as to make an output amplitude constant and, thereafter, the signal is sent to the A/D converter 4. The one of the video signals is supplied as a chrominance signal (C signal) to the chroma demodulating circuit 3 and is demodulated into an I (R-Y) signal and a Q (B-Y) signal. The I and Q signals are similarly sent to the A/D converting circuit 4.
The one of the video signals is supplied as a sync signal to the PLL circuit 7, by which the oscillation is executed at a frequency of 28.6 MHz (=8f.sub.sc :f.sub.sc =3.579545 MHz) as fundamental clocks which are necessary for the double-speed sequential scan, thereby accomplishing the phase lock with a horizontal sync signal.
The A/D converting circuit 4 quantizes and converts the luminance signal into the digital signal at 14.3 MHz (4f.sub.sc) on the basis of 8 bits and 256 gradations. The A/D converting circuit 4 quantizes and converts the C signal into the digital signal at 3.58 MHz (f.sub.sc)) on the basis of 7 bits and 128 gradations. The signal processing circuit 5 receives output signals of the A/D converting circuit 4 and executes various kinds of processes to realize a high picture quality and produces interpolation signals which are necessary for the three-dimensional Y/C separation, motion detection, and double-speed sequential scan. In the above case, the signal processing circuit 5 generates the luminance signal and the chrominance signal of the present line and the luminance signal and the chrominance signal of the interpolation line. The horizontal frequency until the above stage is set to 15.75 kHz.
The memory circuit 6 is a circuit which is necessary to execute the double-speed sequential scan by receiving the processes of the signal processing circuit 4. The writing operation into the memory is executed every scan (1H) by the clocks of 14.3 MHz. The reading operation from the memory is performed at a frequency of 28.6 MHz by alternately reading out data from the present line and the interpolation line. By synthesizing both of the data which have been read out, the double-speed sequential scan is realized. In the above process, the horizontal frequency is set to 31.5 kHz.
The control circuit 8 generates various control signals to execute the above operations.
The digital data of the video signal whose speed has been doubled by the memory circuit 6 is supplied to the D/A converting circuit 9 and is converted into the analog signal, so that the luminance signal 2Y and the chrominance signals 2I and 2Q are generated. By receiving those signals, the matrix circuit 10 converts them into the primary color signals of R, G and B.
By supplying those RGB output signals to the screen of the CRT or VPS, a clear video image without a line flicker and a dot interference is displayed.
The EDTV as mentioned above can have the following functions.
Ordinarily, in the video signal of the NTSC system, the aspect ratio is set to 4:3. However, there is considered a function such that the size in the horizontal direction of the video image is compressed into 12/16 as shown in FIG. 2 and the video image having the aspect ratio of 4:3 is displayed on the CRT or screen which has been deflected at a wide aspect ratio such as 9:16 or the like. If the video signal of the aspect ratio of 4:3 is directly displayed by the TV receiver having the aspect ratio of 9:16, the video image which has been compressed in the vertical direction is displayed.
As such compressing means can be realized by changing a horizontal deflection current (changing an amplitude) or can be also electrically realized by using memories.
FIG. 3 shows a block diagram of a compression processing circuit using memories. Explanation will now be made with respect to the luminance signal. The same shall also apply to the chrominance signal.
Reference numerals 61 and 64 denote simple memories for the double-speed scan. The memory circuit 6 in FIG. 1 has the above construction. Reference numerals 62, 63, 65, and 66 denote memories to further compress the double-speed data. The reason why two memories are provided for each of the memories 61 and 64 is because the data is divided into the halves and processed since the operating speed cannot be accomplished by the single memory (the reading speed is higher than the writing speed). Reference numeral 67 denotes a control circuit to control the writing and reading operations for the memories 62, 63, 65, and 66; 68 a synthesizing circuit to synthesize outputs of the memories 62, 63, 65, and 66; and 69 a switching circuit for switching the double-speed data from the memories 61 and 64 and the compression data from the synthesizing circuit 68 and for generating either of the those data.
The operation will now be briefly explained hereinbelow with reference to timing charts of FIGS. 5 and 6.
First, as a memory, there is used a line memory of the FiFo type of (910 bits.times.8) of .mu.PD42101C made by NEC Corporation shown in FIG. 4 in which the writing and reading operations can be fundamentally asynchronously executed. In FIG. 4, WCK denotes a write clock signal; RCK a read clock signal; WE a write enable signal; RE a read enable signal; WRST a write reset signal; and RRST a read reset signal. Those signals are obtained from the control circuits 67 and 80.
The relation between the quantizing frequency (4f.sub.sc) and a horizontal frequency (f.sub.h =15.75 kHz) is set to just 910. Address counters are independently provided for writing and for reading and are reset to 0 by the reset signals (write: WRST, read: RRST) and automatically count clocks until 910. The ordinary double-speed conversion is executed in the following manner. As shown in FIG. 6, after the address counters of the memories 61 and 64 were reset by the write reset signals WRST, the present line signal (present.multidot.Y) of a 15.75 kHz rate is written into the memory 61 and the interpolation line signal (interpolation.multidot.Y) is written into the memory 64 by the clocks WCK of 14.3 MHz )4f.sub.sc) by the signal processing circuit 5. On the other hand, after the memories 61 and 64 were reset by the read reset signal RRST with a delay time of 0.5H, the reading operations are alternately performed by the clocks RCK of 28.6 MHz (8f.sub.sc) and the present read enable signal REAL and the interpolation read enable signal REAL. 2 present.multidot.Y.sub.s and 2 interpolation.multidot.Y.sub.s are obtained for 1H period of time and are synthesized, thereby obtaining a double-speed converted luminance signal 2Y.sub.s .
FIG. 6 shows the case of further compressing. The double-speed converted luminance signals (2 present.multidot.Y.sub.s, 2 interpolation.multidot.Y.sub.s) are written by the clocks of 8f.sub.sc =28.6 MHz (actually, the clock frequency is set to 4f.sub.sc =14.3 MHz in consideration of the speed of the memory and, as mentioned above, the memory for the present line and the memory for the interpolation line are independently provided and the processes are executed) and are read out by the clocks f.sub.w higher than the above frequency. To display the video image of the aspect ratio of 4:3 as shown in FIG. 2, the reading clock f.sub.w is set to 8f.sub.sc .times.16/12 [MHz]. Further, by controlling by the read enable signal present RE and read enable signal interpolation RE each having a width of 910 bits in a manner such that the read-out image is located at the center of the screen of the CRT, a luminance signal 2Y.sub.w whose time base has been compressed can be obtained.
In the conventional example, the reason why the circuit for the double-speed sequential scan and the circuit for the time base compression are independently provided is because there is a limitation in the reading speed in order to execute the reading operation earlier than the writing operation (so that the reading operation does not outrun the writing operation). The number of memories is large and a peripheral construction is also complicated.